1. Field of the Invention
The invention relates to a method for remotely measuring the level of a bulk material in a vessel. The method of the invention is particularly useful for remotely measuring the level of radioactive resin material which is temporarily stored in spent resin storage tanks so that the inventory of such radioactive resin material can be positively established.
2. Description of the Prior Art
In the normal operation of a nuclear reactor power plant, radioactive fission and corrosion products are generated by the reactor and transported by the reactor coolant. In order to maintain the radioactivity of the reactor coolant within an acceptable level, the reactor coolant is processed through various resins and filters. Over a period of time the efficiency of the resin for removing radioactivity from the coolant decreases and the resin must be replaced. Because the accumulated radioactivity in the resin results in radiation levels on the order of 1000 roentgens per hour, removal is accomplished remotely by flushing the resin from its container to a spent resin storage vessel.
The spent resin storage vessel is located on the site of the nuclear power plant and provides only temporary storage for the spent resin. Periodically the spent resin is emptied from the storage vessels and packed into shielded drums which are shipped away from the site of the nuclear power plant to a permanent storage location.
In order for plant operators to establish when a spent resin vessel should be emptied into shielded drums, and to determine the number of drums required in such an operation, it is necessary to have a means for positively establishing the inventory of spent resin in the spent resin storage vessel. However, because of the high radiation levels associated with spent resin, direct means are not available for measuring the level of the spent resin in the vessel.
In the past, various indirect techniques have been utilized to maintain inventory control of spent resin. For example, load cells have been used to measure the weight of the vessel as it is being filled with spent resin. By knowing the weight of the vessel when it is empty, the net weight of the spent resin can be obtained, from which, with a knowledge of the density of the resin, the volume of the resin can be derived. The use of load cells for maintaining inventory control, however, has proven to be ineffective because, among other reasons, the use of load cells has not produced the required accuracy. Another indirect technique for maintaining inventory control of spent resin is to maintain accurate records of all resins entering and leaving the nuclear plant. Such administrative procedures are time consuming and subject to error.